A disk drive is a data storage device that stores data in concentric tracks on a disk shaped medium. Data is read from the medium by spinning the medium about a central axis while positioning a transducer near a desired track of the medium to sense the data. The transducer provides an electrical signal representative of the sensed data to data processing circuitry within the disk drive which converts the electrical signal to a format that is recognizable by an attached host unit. The converted data signal is then delivered to the host unit for use by it. Disk drives can store data in any of a number of different forms, such as magnetic data storage and optical data storage.
Disk drive units are enclosed within a housing to mitigate the effects of vapor, particulate and contamination on the workings of the drive. As can be appreciated, undesirable substances like these exist both inside and outside the disk drive housing and can have a deleterious effect on the operation of the drive. For example, particles and volatile gases can result in performance problems such as stiction between the transducer and the disk, creation of thermal asperities, and even transducer crashes. To reduce such occurrences, the level of airborne particles and gases within the disk drive housing should be kept low.
The environment inside a disk drive housing can be dynamic due to the creation of pressure gradients. Pressure gradients can be the result of heating or cooling, from internal or external sources, or the spinning up or down of the disks within the housing. As a result, convection may drive air out of or draw it into the drive housing through a predetermined path, such as through a filter and breather hole, or through undesirable paths such as leaks around gaskets and screw holes. In addition to contaminant movement by air flow or convection, contaminants may also be moved by diffusion. Diffusion is the time and temperature dependent transport of material in response to a chemical gradient. Diffusion may occur inside the drive or between the inside and outside of the drive depending upon the presence of a chemical gradient.
Filters have been designed to reduce the levels of undesired substances introduced into the housing of a disk drive, including multi-functional filters to filter undesired chemical vapors and particles. In many instances, these multi-functional filters are attached to the inside of the drive housing adjacent an opening in the cover or base plate. The filter is typically attached with an adhesive. In such a configuration, the reliability of the drive may be affected by the reliability of the adhesive joint connecting the filter to the inside of the drive housing. Failure of the adhesive may result in an influx of uncontrolled contamination and may potentially cause physical damage to the disk drive due to movement of the loose filter.
A specific example of a multi-functional filter for a disk drive assembly is disclosed in U.S. Pat. No. 5,030,260, issued Jul. 9, 1991, which discloses an intricate multi-piece filter assembly comprising a number of component layers through which incoming air is filtered, including external tape 25, diffusion plate 36, a first particulate filter 31, a first chemical adsorbent 33, a second chemical adsorbent 34, a second particulate filter 32, and bottom housing 30, including a second diffusion path 52 and bottom cover 39. However, there are numerous drawbacks associated with this design.
In particular, as the '260 patent is generally directed to a mainframe or other high end application, it does not recognize or address many issues resulting from the development of smaller and less expensive, yet more complicated and faster disk drive assemblies, particularly for use in smaller computers, such as personal computers, laptops and still smaller computers. For example, in a mainframe environment, disk drive assemblies are not to be subject to the rigorous form factor limitations of a disk drive assembly in a typical desktop, laptop or smaller computer. As shown in FIG. 3 of the '260 patent, at least a portion of the filter extends above the top cover of the disk drive assembly. This alignment would violate form factor requirements of maintaining a flush top cover surface in desktop, laptop and smaller computers. The '260 patent also discloses positioning the filter directly over the disk stack where very little space exists in a disk drive used in a personal computer.
Another drawback of the filter design disclosed in the '260 patent is that the filter is expressly designed to filter only incoming air and avoid filtering outgoing air and vapors, such as outgases from adhesives and the like. This one way restriction on air flow appears to be due to the limited size and capacity of the chemical adsorbent, perhaps due to its position above the disk stack where space is limited. Indeed, because of the limited size and capacity of the chemical adsorbent, the '260 patent discloses positioning a diffusion path on each side of the chemical adsorbent to inhibit diffusion and avoid premature depletion of the capacity of the chemical adsorbent.
Additionally, the '260 patent does not disclose a filter that can be removed and reused to accommodate reworking the disk drive assembly or to maximize the flexibility of the assembly and testing process. Because the diffusion paths appear to be positioned at the surface of the filter body, removing the outer tape seal to remove the filter to permit reworking of the drive would likely irreparably damage the diffusion path and require that the filter be replaced with a new filter. Moreover, many if not most commercial drives are electrically and mechanically tested before being shipped from the manufacturer. In certain circumstances, drives fail and must be reworked. In those instances, the drive must be opened and, as a result, the filter is exposed to a greater volume of air, without anything inhibiting diffusion. If unprotected, this causes a premature depletion of the chemical adsorbent capacity, potentially decreasing or reducing drive reliability if the filter is reused. Removing the filter further allows the cover to be cleaned, after testing but before commercial shipment, without damage to the filter or disassembly of the drive.
With the development of smaller, less expensive disk drive assemblies, a need exists for an improved multi-functional filter to clean interior and incoming air of vapors, particles and other contaminants. This filter is capable of installation at any time during the manufacturing process, including following testing and removal, and may be reused after rework of the disk drive assembly.